s6 c6

I have a facelift C6 2.0 TDI 170bhp. I’ve found S6 C6 Brakes. I’ve read I only need to change the spindles to make them work. Is a spindle what I’d call a wheel hub (as pictured)? why do the S6 brakes need a new spindle? Is it to accommodate the disks? If so would I need different alloys? kind...